Melatonin for Sleep: How It Works, What It Does and What It Can't

TL;DR

• Melatonin is a hormone your pineal gland releases as darkness falls. It tells the body that biological night has started. It does not generate sleep.
• Ordinary room light in the evening delayed melatonin onset in 99 percent of people and shortened its duration by about 90 minutes in a controlled study.
• In the EU it has two authorised claims: it contributes to the reduction of the time taken to fall asleep (1 mg before bed) and to the alleviation of subjective feelings of jet lag (0.5 mg on travel days).
• A meta-analysis found it shortened sleep onset by about 12 minutes overall, by about 39 minutes in people with a delayed sleep phase, and by about 7 minutes in people with insomnia.
• It suits circadian problems: jet lag, shift work, a late body clock. For other kinds of poor sleep the evidence points elsewhere.

Melatonin is the most reached-for sleep supplement in the world, and one of the most misunderstood. Most people take it like a sleeping pill, in large doses, when they want to feel drowsy. That is not what it does. Knowing what it does changes how you use it and why it so often disappoints.

What melatonin is

Melatonin is a hormone made by the pineal gland, a small structure deep in the brain. It is synthesised from serotonin and released in response to darkness. Its job is to announce that night has arrived. In response to that announcement, processes calibrated to happen at night begin: core temperature drops, cortisol stays low, and the circadian clock takes its cue (Arendt 2006).

Melatonin sets the timing of sleep. It does not produce sleep on its own. That distinction explains almost everything else on this page.

How your body makes it, and what light does to it

The process starts in the eye. Photoreceptors in the retina relay ambient light levels to the suprachiasmatic nucleus, the master clock in the hypothalamus. During the day the clock suppresses melatonin production. As light fades in the evening the suppression lifts and the pineal gland starts releasing it. Levels rise a couple of hours before habitual bedtime, peak in the middle of the night and fall toward morning.

The system is sensitive to light. In a study of 116 healthy adults living in a research centre, exposure to ordinary room light in the eight hours before bedtime, compared with dim light, produced a later melatonin onset in 99 percent of individuals and shortened melatonin duration by about 90 minutes. Room light during the usual hours of sleep suppressed melatonin by more than 50 percent in 85 percent of trials (Gooley 2011). That study is the reason for the advice to dim your environment in the evening. The light side of this sits in blue light and sleep, and the clock side in circadian rhythm explained.

Taken as a supplement, melatonin adds to the body's own signal. It tells the clock that night has arrived, which is why timing matters as much as dose.

What the authorised claims say

Melatonin is one of the few sleep-related substances with authorised EU health claims, and both are narrow. Under the EU Register of nutrition and health claims, melatonin contributes to the reduction of the time taken to fall asleep, a claim that applies at 1 mg taken close to bedtime. Melatonin also contributes to the alleviation of subjective feelings of jet lag, which applies at a minimum of 0.5 mg taken close to bedtime on the first day of travel and the following few days.

Both claims are about sleep onset and timing. Neither is about depth or duration of sleep.

What the trials measured

A meta-analysis of randomized trials in primary sleep disorders found that melatonin shortened sleep onset latency by 11.7 minutes overall. In people with delayed sleep phase syndrome the figure was 38.8 minutes, which the authors called clinically important. In people with insomnia it was 7.2 minutes. The authors concluded that melatonin is not effective for most primary sleep disorders with short-term use, with delayed sleep phase the exception, and that it is safe with short-term use (Buscemi 2005).

That matches the mechanism. A timing signal helps most when the timing is the problem.

The dose question

Your body produces a small amount of melatonin each night, with blood levels peaking at a fraction of a nanogram per millilitre. Most over-the-counter products sell 3, 5 or 10 mg tablets, many times the physiological amount.

The research behind the authorised claims sits at 0.5 to 1 mg, and the claims only apply at those doses. Nothing in the trial literature shows the 5 and 10 mg products on shelves doing more for sleep onset than 1 mg does. Higher doses are linked to morning grogginess, covered in melatonin side effects.

When melatonin helps

Because it works by shifting circadian timing, melatonin is most useful when the problem is circadian.

Jet lag is the clearest case. A low dose at the destination bedtime for the first few days helps the clock move to the new schedule, and that use has an authorised claim behind it.

Shift work follows the same logic. Workers who need to sleep at a time that conflicts with their natural phase can use melatonin as a timing cue.

A late body clock, where someone's natural bedtime sits hours after a conventional one, responds to small doses taken a few hours before the desired sleep time, since the goal is to pull the clock earlier rather than to sedate (Arendt 2006).

What it can't do

Taking 5 mg every night because you have trouble sleeping is a category error. The problem for most people with poor sleep is a mix of irregular timing, evening light, stress and not enough sleep pressure. Melatonin addresses none of those. For the compounds people turn to when timing isn't the issue, see melatonin alternatives.

Regulation is worth knowing too. In much of Europe, melatonin above a certain dose is a prescription medicine, so availability and legal dose vary by country. Anyone who is pregnant, breastfeeding, taking medication or managing a health condition should check with a healthcare professional before using it.

Frequently asked questions

Does melatonin help you sleep?

At low doses taken at the right time, melatonin contributes to the reduction of the time taken to fall asleep, which is an authorised EU claim. In the pooled trials that meant about 12 minutes overall, 39 minutes for people with a delayed sleep phase and 7 minutes for people with insomnia (Buscemi 2005). It is a timing signal and suits circadian problems.

How much melatonin should I take?

The authorised claims sit at 0.5 to 1 mg, taken close to bedtime. The trials behind them used low doses, and nothing shows the high-dose tablets doing more.

Is melatonin a sleeping pill?

No. It announces biological night and shifts the body clock. It does not sedate.

Does room light affect melatonin?

Yes. Ordinary room light in the evening delayed melatonin onset in almost everyone and shortened its duration by about 90 minutes in a controlled study (Gooley 2011). Dim light in the evening protects your own melatonin before any supplement comes into it.

Is melatonin safe?

At low doses it has a good short-term safety record in the trials. In much of Europe higher-dose melatonin is a prescription medicine. Check with a professional if you are pregnant, breastfeeding, on medication or managing a condition.

Disclaimer

This article is for general information only. It is not medical advice and it does not replace guidance from a qualified healthcare professional. Melatonin is regulated differently across countries and doses. If you are pregnant, breastfeeding, taking medication or living with a health condition, speak with a qualified healthcare professional before using it. Do not use this information to diagnose or treat any condition.